U.S. patent number 5,874,804 [Application Number 08/807,974] was granted by the patent office on 1999-02-23 for organic electroluminescent device hermetic encapsulation package and method of fabrication.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Stephen P. Rogers.
United States Patent |
5,874,804 |
Rogers |
February 23, 1999 |
Organic electroluminescent device hermetic encapsulation package
and method of fabrication
Abstract
An organic electroluminescent device encapsulating package
including a substrate, an organic electroluminescent device carried
by the substrate, an inorganic perimetric seal carried by the
substrate, the perimetric seal encircling the organic
electroluminescent device within a perimeter thereof, and an
inorganic cover overlying the organic electroluminescent device and
sealingly coupled to the substrate in a spaced apart relationship
by the inorganic perimetric seal.
Inventors: |
Rogers; Stephen P. (Phoenix,
AZ) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
|
Family
ID: |
25197562 |
Appl.
No.: |
08/807,974 |
Filed: |
March 3, 1997 |
Current U.S.
Class: |
313/512; 313/504;
313/506 |
Current CPC
Class: |
H05B
33/04 (20130101); H01L 51/5246 (20130101); H01L
51/5243 (20130101) |
Current International
Class: |
H01L
51/50 (20060101); H01L 51/52 (20060101); H05B
33/04 (20060101); H05B 033/04 () |
Field of
Search: |
;313/506,512,504 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Patel; Nimeshkumar D.
Attorney, Agent or Firm: Parsons; Eugene A. Koch; William
E.
Claims
Having fully described the invention in such clear and concise
terms as to enable those skilled in the art to understand and
practice the same, the invention claimed is:
1. An organic electroluminescent device encapsulating package
comprising:
a substrate;
an organic electroluminescent device carried by the substrate;
an inorganic perimetric seal carried by the substrate, the
perimetric seal encircling the organic electroluminescent device
within a perimeter thereof; and
an inorganic cover overlying the organic electroluminescent device
and sealingly coupled to the substrate in a spaced apart
relationship by the inorganic perimetric seal, and the inorganic
perimetric seal including a first layer of low melting metal
patterned on the substrate and a second layer of low melting metal
patterned on the cover, the first layer and the second layer joined
by reflow of the low melting metal.
2. An organic electroluminescent device encapsulation package as
claimed in claim 1 wherein the perimetric seal further includes a
first adhesion layer coupling the first layer to the substrate and
a second adhesion layer coupling the second layer to the cover.
3. An organic electroluminescent device encapsulation package as
claimed in claim 1 wherein the cover and the substrate include
contacts electrically coupled to the organic electroluminescent
device.
4. An organic electroluminescent device encapsulation package as
claimed in claim 1 wherein the organic electroluminescent device
includes a first electrical contact layer formed on the substrate
and an organic layer overlying the first electrical contact layer
and carried by the substrate, the perimetric seal overlying the
first electrical contact layer and carried by the substrate.
5. An organic electroluminescent device encapsulation package as
claimed in claim 4 wherein the organic electroluminescent device
further includes a second electrical contact layer overlying the
organic layer and the first electrical contact layer.
6. An organic electroluminescent device encapsulation package as
claimed in claim 5 wherein the perimetric seal has a thickness
substantially equal to the thickness of the organic layer such that
the first electrical contact layer and the second electrical
contact layer are spaced apart sufficient to accommodate the
organic layer while maintaining contact therewith.
7. An organic electroluminescent device encapsulating package
comprising:
a substrate;
a first electrical contact layer formed on the substrate;
an organic layer overlying the first electrical contact layer and
carried by the substrate;
a perimetric seal overlying the first electrical contact layer and
carried by the substrate, the perimetric seal enclosing the organic
layer within a perimeter thereof;
a second electrical contact layer overlying the organic layer and
the first electrical contact layer, the perimetric seal has a
thickness substantially equal to the thickness of the organic layer
such that the first electrical contact layer and the second
electrical contact layer are spaced apart sufficient to accommodate
the organic layer while maintaining contact therewith; and
an inorganic cover overlying the second electrical contact layer,
the organic layer and the first electrical contact layer, the
inorganic cover is carried by the substrate and supported in a
spaced apart relationship therefrom and sealed thereto by the
perimetric seal, and the perimetric seal including a first layer of
a first metal patterned on the substrate overlying the first
electrical contact layer and a second layer of a second metal
patterned on the cover, the first layer and the second layer being
joined by pressure to form the perimetric seal.
8. An organic electroluminescent device encapsulating package as
claimed in claim 7 wherein the first metal includes one of indium
and gold and the second metal includes another of indium and
gold.
9. An organic electroluminescent device encapsulation package
comprising
a substrate;
a first electrical contact layer formed on the substrate;
an organic layer overlying the first electrical contact layer and
carried by the substrate;
a perimetric seal overlying the first electrical contact layer and
carried by the substrate, the perimetric seal enclosing the organic
layer within a perimeter thereof;
a second electrical contact layer overlying the organic layer and
the first electrical contact layer, the perimetric seal has a
thickness substantially equal to the thickness of the organic layer
such that the first electrical contact layer and the second
electrical contact layer are spaced apart sufficient to accommodate
the organic layer while maintaining contact therewith; and
an inorganic cover overlying the second electrical contact layer,
the organic layer and the first electrical contact layer, the
inorganic cover is carried by the substrate and supported in a
spaced apart relationship therefrom and sealed thereto by the
perimetric seal, wherein the perimetric seal includes a first layer
of low melting metal patterned on the substrate overlying the first
electrical contact layer and a second layer of low melting metal
patterned on the cover, the first layer and the second layer being
joined by reflow of the low melting metal.
10. An organic electroluminescent device encapsulation package as
claimed in claim 9 wherein the perimetric seal further includes a
first adhesion layer coupling the first layer to the substrate and
a second adhesion layer coupling the second layer to the cover.
11. An organic electroluminescent device encapsulation package as
claimed in claim 10 wherein the adhesion layer includes titanium,
and the perimetric seal includes indium.
Description
FIELD OF THE INVENTION
The present invention pertains to organic electroluminescent
devices and more specifically to hermetic encapsulation of organic
electroluminescent devices.
BACKGROUND OF THE INVENTION
Organic electroluminescent devices (OEDs), and especially organic
light emitting diodes (LEDs) and the like, generally utilize a
layer of reactive metal in the cathode to ensure efficient
injection of electrons and low operating voltages. However,
reactive metals are particularly susceptible to damage due to
oxidation in the presence of oxygen and moisture. Oxidation of the
metal severely limits the lifetime of a device. A hermetic seal is
normally required to achieve long term stability and longevity. For
example, the time to half the luminance intensity under constant
current condition for an unencapsulated device versus an
encapsulated device is 200 hours as opposed to 1000 hours. Also,
the rate of dark spot growth is significantly reduced for
encapsulated devices.
Several approaches to protecting or encapsulating OEDs have been
reported. In a prior art (JP 91359134), a glass cover was directly
adhered to the OED active area and device substrate with a photo
curing resin layer. Another prior art (U.S. Pat. No. 5,189,405),
used a series of sheets inside a cover laminate consisting of a
metallic foil between two organic resin films adhered to the OED
glass substrate using an epoxy resin. Typically, a low temperature,
thermally cured organic epoxy material is used to create the
perimeter seal or barrier and adhere the cover to the device
substrate, and is usually accomplished by curing the organic epoxy
at 85 degrees Celsius over a two hour period. Furthermore, the
permeation rate of oxygen and water through organic barriers is
several orders of magnitude greater than through inorganic
barriers. Thus, the organic epoxy provides a path for the ingress
of oxygen and water. A further problem is a result of the fact that
the organic layers, particularly the hole transport materials are
sensitive to temperatures as related to their property of glass
transition. The glass transition is best described as a molten
solid, and for many organic materials occurs at relatively low
temperatures, such as below 100 degrees Celsius. The potential for
the organic material to crystallize is greater once the glass
transition has been reached. Crystallization of an organic film in
the fabrication of an OED leads to low charge mobility, charge
traps, pinholes and shorts. In many instances, even approaching the
critical temperatures of the organic layers, especially if the
elevated temperatures are maintained for relatively long periods of
time, can degrade the organic material and reduce the reliability
and/or the longevity of the device.
Several integrated approaches have also been developed. The
integrated approaches typically include a protection layer
deposited on the discrete device as part of the fabrication
process. The integrated encapsulation schemes require specialized
processing equipment and techniques.
Accordingly, it is highly desirable to devise a relatively
inexpensive and convenient encapsulation package for hermetically
sealing organic electroluminescent devices.
It is a purpose of the present invention to provide a new and
improved encapsulation package for organic electroluminescent
devices.
It is another purpose of the present invention to provide a new and
improved encapsulation package for organic electroluminescent
devices which has a thin profile and is light in weight.
It is a further purpose of the present invention to provide an
encapsulation package for organic electroluminescent devices which
acts as an effective barrier to oxygen and moisture.
SUMMARY OF THE INVENTION
Briefly, to achieve the desired objects of the instant invention in
accordance with a preferred embodiment thereof, provided is an
organic electroluminescent device encapsulating package including a
substrate, an organic electroluminescent device carried by the
substrate, an inorganic perimetric seal carried by the substrate,
the perimetric seal encircling the organic electroluminescent
device within a perimeter thereof, and an inorganic cover overlying
the organic electroluminescent device and sealingly coupled to the
substrate in a spaced apart relationship by the inorganic
perimetric seal.
Also provided is a method of fabricating an organic
electroluminescent device encapsulating package.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and further and more specific objects and advantages
of the instant invention will become readily apparent to those
skilled in the art from the following detailed description of a
preferred embodiment thereof taken in conjunction with the
drawings, in which:
FIG. 1 is a simplified cross-sectional view of an organic
electroluminescent device encapsulation package; and
FIG. 2 is a partial sectional side view of the organic
electroluminescent device of FIG. 1, illustrating the perimetric
seal and placement of the cover.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning to the drawings in which like reference characters indicate
corresponding elements through out the several views, attention is
first directed to FIG. 1 which illustrates a simplified
cross-sectional view of a hermetically sealed encapsulation package
10, in accordance with the present invention. Package 10 includes a
supporting substrate 12 which is some optically clear material,
such as glass, quartz, a transparent semiconductor material or the
like, etc. An organic electroluminescent device 14 is positioned on
substrate 12, generally by fabricating device 14 directly on
substrate 12 in any of the various methods of fabricating organic
electroluminescent devices.
As a specific example, device 14 includes a transparent first
electrical contact layer 16 of conductive material, such as
indium-tin-oxide (ITO) or the like, with an active organic layer
18, typically composed of a laminant of several organic layers
which function to inject holes and electrons from opposite
contacts, transport holes and electrons, and form a recombinant or
electroluminescent zone to form the organic electroluminescent
device, positioned thereon and a second electrical contact 20
formed of a metal layer including a thin layer of a reactive metal.
As previously stated, device 14, and especially the layer of
reactive metal, is susceptible to oxygen and moisture in the
surrounding atmosphere and must, therefore, be protected to provide
reliability and a reasonable operating longevity.
Protection is provided in the form of an inorganic cover 22 having
an inner surface 23 and an edge 24. Inorganic cover 22 is formed of
an electrically insulating inorganic material, preferably glass,
quartz, or semiconductor material, as oxygen and water permeate
inorganic materials at a rate which is orders of magnitude less
than the rate at which oxygen and water permeate organic materials
such as thin plastic films. The use of glass, quartz or thin
silicon provides an inexpensive material having light weight and
low profile.
Inorganic cover 22 overlies organic electroluminescent device 14
and is sealingly coupled to the substrate in a spaced apart
relationship by a perimetric seal 25. Perimetric seal 25 completely
encircles organic electroluminescent device 14 or a multiplicity of
organic electroluminescent devices 14 in an array within a
perimeter thereof, providing a hermetic seal between cover 22 and
substrate 12. Perimetric seal 25 is formed of inorganic materials,
as oxygen and water permeate inorganic material at a rate which is
orders of magnitude less than the rate at which oxygen and water
permeate organic materials such as the epoxies typically used in
bonding.
With additional reference to FIG. 2, the process of encapsulation
includes creating inorganic perimetric seal 25 between substrate 12
and inorganic cover 22. Inorganic perimetric seal 25 is created by
forming a first layer 30 of low melting metal on substrate 12 and
forming a second layer 32 of low melting metal on inner surface 23
of cover 22 proximate edge 24. Cover 22 is then positioned
overlying organic electroluminescent device 14 with second layer 32
overlying first layer 30 and moved into contact in a direction
illustrated by arrowed line A. Inorganic perimetric seal 25 is
created by reflowing first layer 30 and second layer 32 in an inert
and dry environment. Reflow of first layer 30 and second layer 32
can be accomplished in a variety of manners, but is preferably
accomplished by using pressure and a heating element having the
same pattern as inorganic perimetric seal 25. The temperature for
the reflow process is confined to the proximity of inorganic
perimetric seal 25 and the time for the reflow process is
significantly less than the time required to thermally cure the
conventional epoxy due to low temperature alloying or diffusion
bonding created by the pressure sealing process. Thus, the exposure
of the temperature sensitive organic material to heat is
significantly reduced.
Still referring to FIG. 2, perimetric seal 25 further includes a
first adhesion layer 33 coupling first layer 30 to substrate 12 and
a second adhesion layer 34 coupling second layer 32 to cover 22. In
the preferred embodiment, first layer 30 and second layer 32-are
formed of indium. However, indium does not adhere well to the
materials of substrate 12 and cover 22. Therefore, adhesion layers
33 and 34, formed of titanium, are employed. It will be understood
that other materials can be used, specifically, tin and indium or
gold and indium material systems may be employed whereby first
layer 30 is formed of tin or gold and second layer 32 is formed of
indium. Alternatively, first layer 30 is formed of indium and
second layer 32 is formed of tin or gold. Including indium in first
layer 30 and gold in second layer 32, for example, allows a
satisfactory joining or amalgamation by the application of a
relatively light pressure therebetween.
As can be seen in FIGS. 1 and 2, first adhesion layer 33 and first
layer 30 are formed overlying first contact 16 patterned on
substrate 12. In this manner, electrical contact outside package 10
can be accomplished. However, a short will develop if perimeter
seal 25 directly contacts electrical contact 16. Therefore, in
addition, in this specific embodiment, an electrically insulating
layer 35 of dielectric material such as a PECVD nitride or oxide is
deposited between first adhesion layer 33 and substrate 12,
insulating electrical contact 16 from first adhesion layer 33,
first layer 30 and second layer 32.
Thus, a relatively inexpensive and convenient encapsulation package
for hermetically sealing organic electroluminescent devices has
been provided. The encapsulation package for organic
electroluminescent devices has a thin profile, is light in weight,
and provides an effective barrier to oxygen and moisture.
Various changes and modifications to the embodiments herein chosen
for purposes of illustration will readily occur to those skilled in
the art. To the extent that such modifications and variations do
not depart from the spirit of the invention, they are intended to
be included within the scope thereof which is assessed only by a
fair interpretation of the following claims.
* * * * *